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Electric Current

Science, Grade 6


Table Of Contents: Electric Current

1. What is Electric Current?
The continuous flow of electric charges through a wire or similar material is called electric current. Imagine electric charges moving at a steady rate through a wire. You can count how many charges move past a given point during a certain period of time. If the charges start to flow more quickly, you would count more charges moving past the same point over the same amount of time. Therefore, the rate of flow, or the rate of the current, has increased.
2. Current Is Measured in Amps
The rate of flow of electrical charges, or current, is expressed in amperes, also called amps. The capital letter A is used to symbolize this unit. In equations, amps are symbolized by the capital letter I. Marie Ampere was a French physicist who lived in the early 1800s and is known for his extensive research in electromagnetism.
3. Two Types of Electrical Current
There are two types of electric current, DC and AC. The charges in DC, or direct current, always flow in the same direction. The charges in AC, or alternating current, flow one way and then flow the other way. They are continuously reversing direction. Many batteries produce DC electricity. You can find DC batteries in cell phones, cameras, and even cars. Electric appliances around the house such as microwaves, televisions and washing machines use AC electricity.
4. Direct Current vs. Alternating Current
Two famous scientists, Thomas Edison and Nikola Tesla, were both interested in developing electrical supply and power systems. Edison was a strong proponent of direct current (DC) systems while Tesla supported alternating current (AC) systems. Today, in our homes, the electrical power is supplied using alternating current because it is easier to safely control the voltage of this type of current.
5. Electricity in Circuits
An electric circuit is a complete path that electricity flows through. For electrical current to continuously flow, the charges must move through a path that is unbroken. This continuous flow of current within a circuit enables us to use electrical power. Our homes and machines use a variety of electric circuits.
6. Voltage
Electric currents will flow in a wire, as long as there is voltage. Voltage is the potential difference between two points in a circuit. Another way to think about it is the amount of energy released as a charge moves between these two points. Voltage is measured in units called volts. In equations voltage is symbolized by the letter V. The greater the voltage is, the higher the current. For example, a 1.5-volt battery used in a camera produces less electrical current than a 12-volt battery used in a car.
7. Electrical Resistance
An electrical current is affected by the resistance of the material it is flowing through. Resistance is measured in units called ohms, symbolized by the Greek letter omega. In equations, resistance is symbolized with an R. If the voltage remains the same, increasing the resistance will result in a decrease in the current.
8. Resistance Factors-Material
Factors that affect resistance include an objects material, temperature, length and thickness. Materials that are good conductors have less resistance, because their electrons are held loosely on the atoms. Materials that are good insulators have a higher resistance because their electrons are held tightly together, and electrical charges have difficulty moving.
9. Resistance Factors-Temperature
Some materials will increase in resistance as the temperature increases. The copper atoms within a wire move faster as they gain thermal energy. This increased molecular movement creates resistance by slowing down the flow of electric charges through the wire.
10. Resistance Factors-Length and Thickness
A wires length and thickness affect resistance. Longer wires produce more resistance than shorter wires. As the electrical charges move through the length of the wire, they slow down as they collide with the walls of the wire. Thinner wires are more resistant than thicker wires. Thin wires have less area for the charges to flow through, and therefore the current is slower than thick wires.
11. Ohms Law
Georg Ohm, a Bavarian mathematician and physicist, defined the relationship between resistance, voltage and current. The formula for this relationship, known as Ohms Law, is resistance is equal to voltage divided by the current. For example, if the voltage of a toaster is 120 volts and the current is 12 amps, then the resistance of the toaster is 10 ohms.
12. Electric Power
Machines and appliances transform electrical energy into other types of energy. A stove transforms electricity to heat, and a stereo transforms electricity to sound. The rate at which electrical energy is transformed into another type of energy is called electric power. The unit for electrical power is a watt, and the formula is power equals voltage times current. For example, an electric stove top that uses 240 volts and has a current of 50 amps has 12,000 watts of power.
13. Electricity: Measurements, Units and Symbols
This table is a summary of electric measurements, and their corresponding units, unit symbols and abbreviations in formulas. Lets look at the example of electrical power. If you are referring to the power of a light bulb, then you would use the unit called a watt. You would write 60 watts using a capital W. If you wanted to write out the formula for power, you would use the abbreviation capital P for power.
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